drm: panel: visionox: add backlight dependency

drm: panel: visionox: add backlight dependency

The newly added driver uses the backlight subsystem but is missing the
corresponding Kconfig dependency:

arm-linux-gnueabi-ld: drivers/gpu/drm/panel/panel-visionox-vtdr6130.o: in function `visionox_vtdr6130_probe':
panel-visionox-vtdr6130.c:(.text+0xdee): undefined reference to `devm_backlight_device_register'

Fixes: 65dc9360f741 ("drm: panel: Add Himax HX8394 panel controller driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230117165522.2104380-1-arnd@kernel.org